In addition to MySQL master-slave, you have another choice, Galera

Most Internet companies , All use MySQL Of InnoDB The engine stores data .

To ensure high availability of database , In order to ensure the expansion of performance , Most companies will use Master slave synchronization , Read / write separation Of MySQL Cluster architecture .

Traditional master-slave synchronization , Read / write separation MySQL The cluster architecture is shown in the figure above ：

（1） Main library ： The first instance on the left , Provide an instance of the write service ;

（2） Slave Library ： Two instances on the right , Provide an instance of the read service ;

How does data replication work at this time ？

Still as shown in the figure above ：

（1） The client submits the write operation to the main library ;

（2）Replication： The main library serializes the operation , adopt binlog To the slave library ;

（3） Perform the same sequence of operations from the library , For replica redundancy ;

Traditional master-slave synchronization , Read write separation redundancy mode , What are the problems with database clusters ？

（1） Users should pay attention to cluster details , Implement read-write separation ;

（2） Write library is still single point , Performance cannot be linearly scaled ;

（3） There is a delay in reading the library , Data inconsistency ;

（4） The writing library hung up , From the top of the library , There may be data loss ;

（5） If middleware is introduced ,SQL Ability will be affected ;

（6） O & M complexity ;

（7）…

Since there are so many pain points , Is there a technology , It can solve everyone's problems ？

Galera colony （Galera Cluster） Give birth to .

What is? Galera colony ？

Galera The cluster is based on MySQL InnoDB Synchronous replication ：

（1） Sync ;

（2） Multimaster ;

（3） Database cluster ;

Voice over ： It can support, for example MariaDB Wait for other databases , This article focuses on MySQL.

As shown in the figure above ：

（1）Galera The cluster consists of a set of MySQL The cluster consists of ;

（2）Replication： This group MySQL Server usage Replication plug in To manage database replication ;

（3） The client can read and write to any node in the cluster ;

Galera The official website of the cluster is known as , It and its disadvantages ：

（1） Real multi master （True Multi_Master）, Any data changes will be copied to other nodes ;

（2） There is no such thing as slave latency （slave lag）, Synchronous replication ;

（3） Strong consistency , All nodes are in a consistent state ;

（4） Hot standby , High availability , There is no need to deal with the so-called master-slave failover , There is no need to be empty IP;

（5） No read / write separation is required , You can read and write to any node at any time ;

（6） Support InnoDB;

（7） Transparent to the application ;

（8）…

All in all , In the description on the official website ,Galera Cluster is a highly available , High performance , To ensure data consistency and integrity ：

（1） in the light of MySQL Of ;

（2） Based on synchronous authentication （synchronous certification-based）;

（3） Multiple copies （replication）;

Solution .

online Galera There seems to be less information , Asked some former friends , It doesn't seem to be used much in Internet companies , Ready to write in depth Galera colony , After all, MySQL Another choice after master-slave .

On the official website Galera, What technical points are you interested in ？ Guess how it works ？ Do you think it is necessary to write further ,or Change the subject ？

The comments told me .

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